Modern vehicles require exhaust aftertreatment systems and engine control to achieve emissions levels to comply with various regulations. It is known that aftertreatment systems operate most efficiently under controlled conditions, including operating within appropriate temperature windows. It is desirable to have information regarding an exhaust gas feedstream, including air/fuel ratio and temperature, at multiple locations in an aftertreatment system which is equipped with multiple reactors, catalysts or other emission abatement devices. It is known that engine systems employing lean NOx trap devices (LNT) operate most effectively to trap and regenerate when the LNT is maintained within a narrow range of operating temperatures. It is known that diesel particulate filters (DPF) and selective catalyst reduction systems operate most effectively within a narrow range of operating temperatures.
Known engine control systems utilize one or more gas sensing devices to monitor the exhaust gas feedstream for feedback to the engine system for emissions control and diagnostics. Known gas sensing devices include conventional oxygen sensors, wide-range air/fuel ratio sensors, and exhaust gas constituent sensors, e.g., NOx sensors. A gas sensing device includes a sensing element and an electrically-powered integral heating element. The heating element is used to rapidly heat up and maintain operating temperature of the sensing element within an optimum range of operational temperatures. The sensing element is adapted to monitor oxygen concentration, air/fuel ratio, or other exhaust gas constituents. Known internal combustion engines use one or more gas sensing devices to monitor gases in an exhaust system, an exhaust gas recirculation (EGR) system, and an intake manifold, such as described.
Information regarding the temperature of the exhaust gas feedstream is useful for controlling operation of the engine system to achieve emissions targets, since the effectiveness of a device that treats exhaust gases is dependent upon the operating temperature of the device and the feedstream temperature. A known system for determining the exhaust gas feedstream temperature includes employing a temperature sensor to monitor temperature at a specific location, with the sensor signal output to an electronic control module which controls engine operation. Such a system adds cost, while providing accuracy associated with direct measurement of temperature. Another known system for determining temperature of the exhaust gas feedstream includes algorithms to estimate temperature based upon engine operating conditions and information from existing sensing devices. Such a system incurs limited cost to the system, but requires investment of engineering resources to develop the algorithms and calibration. Furthermore, accuracy of the temperature estimation is known to vary.